Web coating apparatus

ABSTRACT

An apparatus for coating paper, tissue, cardboard, metal foils, thermoplastic films and similar materials includes a hard surfaced raster roll having regularly formed depressions or cells inset into its circumferential surface and over which surface the material to be coated is directed. A portion of the circumferential periphery of the raster roll rotates through an opening in a tank containing a liquid melt of the substance to be coated. The raster roll picks up the liquid melt as its circumferential peripheral surface rotates through the tank and a wiper blade is positioned at the location at which the roll exits from the tank for removing any excess of the liquid melt and retaining it within the tank. The blade has its edge,which contacts the roll,extending toward the roll in the direction opposite to the direction in which the roll rotates. Further, the tank and the wiper blade are mounted for oscillatory or reciprocatory movement relative to the raster roll.

United States Patent 11 1 Herzog 1 Oct. 2, 1973 54] WEB COATINGAPPARATUS 3,169,082 2/l965 Krikorian ll8/4l3 3,511,693 51970 D 'd. 118413x [75] Inventor: Peter Herzog, Fr1bourg, Switzerland [73] Assignee:Polytype AG, Fribourg, Switzerland P im ry Examin rl hn P. MclntoshFiled Feb 24 1972 Attorney-David Toren et al.

[2l] Appl. N0.: 229,003 [57] ABSTRACT Related U S Application Dam Anapparatus for coating paper, tissue, cardboard, 63 I metal foils,thermoplastic films and similar materials I l g l of 1970 includes ahard surfaced raster roll having regularly d one formed depressions orcells inset into its circumferential surface and over which surface thematerial to be Cl 118/212 118/249 a coated is directed. A portion of thecircumferential pc- [5 1 in CI 805C 1/04 riphery of the raster rollrotates through an opening in [58] Fie'ld 407 02 a tank containing aliquid melt of the substance to he 8/409 4 l 26] coated. The raster rollpicks up the liquid melt as its cir- 1 6 cumferential peripheral surfacerotates through the tank and a wiper blade is positioned at the locationat which the roll exits from the tank for removing any ex- [56]References Clted cess of the liquid melt and retaining it within thetank.

UNITED STATES PATENTS The blade has its cdge,which contacts theroll,extend- 2940,8618 6/l960 Patchell ll8/249 X ing toward the roll inthe direction opposite to the di- 3\453-l38 7/1969 i ll8/259 X rectionin which the roll rotates. Further, the tank and 2 1 H1962 y the wiperblade are mounted for oscillatory or reciprogi X catory movementrelative to the raster roll. 2Il701560 8/1939 Hayes 118/261 X 4 Claims,5 Drawing Figures PATENTEDBBT 2mm sum 1 UF 2 FIGZ PATENTEDUBI 2191aSHEET 2 BF 2 FIG. 3

F'IGA- WEB COATING APPARATUS This is a continuation in artapplication ofSer. No. 291 filed January 2, 1970, now abandoned.

SUMMARY OF- THE INVENTION This invention relates in general to apparatusfor coating webs and, in particular, to a new and useful apparatus forcoating material such as paper, tissue, cardboard, thermoplastic film,metal foils such as aluminum and similar material with a highly viscoussubstance which is applied directly to the web by moving the web overthe arcuate surface of a roller which has passed through a reservoir ofthe coating substance.

According to a known method, the coating of webs is effected by means ofa pouring funnel having a nozzle discharge of slot shaped configurationthrough which the molten coating material issues as a curtain either byits own weight or under pressure. The issuing film is applied on the webwhich moves under the nozzle. The slot width of the nozzle generallydetermines the dosage in combination with the applying pressure and thevelocity of the feed of the web. The slightest variation of any one ofthese factors will cause a considerable difference in the amount orweight of material which is deposited on the web. The excess material isusually collected in a tank and then pumped back into the pouringfunnel. The air inclusions formed in the highly viscous melt materialthus is contained in the coating film and accordingly, requires longconditioning zones in order to ensure that the air is removed and doesnot form bubbles. A further disadvantage of the known process is therequirement for high web tensions which are not suitable, for example,for coating very thin webs such as aluminum or other metal foil. Inaddition, with the known method, it is not possible to vary the coatingprocess, for example, to vary the weight of one of the constituents orto vary the quality of the coating, such as its gloss. With the knownmethod, generally, it is possible only to process melts of lowviscosity. Another known arrangement for the coating of webs is effectedby a tank having a slotted nozzle which is arranged under the web; and,as the web is moved over the nozzle, the melt is permitted to ooze upinto the web material which is stretched over the nozzle lip. Theremoval of the excess material of the coating and the equalization ofthe coating surface is effected by steel scrapers arranged behind thenozzle. With this process there is also the likelihood that air will beincluded in the coating because the excess material is pumped back tothe coating tank and transferred to the web by the nozzle. In thisarrangement, it is possible to process relatively highly viscous melts,however, a high web tension is required to obtain even a minimumstripping effect at the nozzle lip. For this reason, the arrangement isnot suitable for applying a coating on tension sensitive webs.

A further known coating arrangement relates to the coating of webs bymeans of oppositely moving, smooth, chromium plated heated steel rolls.The amount of coating is determined by the gap width between the rollsand the melt is fed from a tank located above the nip of the rolls. Adisadvantage of this method is that it is difficult to provide thenecessary circumferential velocities and rotating accuracies of the rolland the velocity of the web fed between them and to construct thearrangement so that there is no sagging between the roll which wouldvary the quantity of coating applied across the web material. Since thevelocity differences of the circumferences of the rolls relative to theweb to be coated are considerable, high residual 1 pressures are formedin the roll gap when highly viscous melts are used. In addition, for arelatively small deposit of coating the rolls must be so closely spacedthat they can be easily damaged. Some attempts have been made to coatweb material by means of a raster roll over which the web material isfed. The raster roll draws the melt by its rotation adjacent the bottomof a tank supply thereof and it delivers the melt under an oscillatingwiper. The wiper strips off the excess of the melt coating so that onlythe raster cups or recesses de-. fined in the raster roll are filled.With highly viscous melts, however, the wiper is pushed away from theroll by the wedging effect of the melt and thus changes the weight ofthe coating being applied. In addition, the film breaks on the rasterroll when using a high viscosity melt and operating at high speed of theraster roll so that the drawing effect is practically cancelled. As aresult, the web is only partly coated. Another disadvantage is therequirement for the heating of the relatively large quantities of themelt material dueto the fact that the melt is a very poor conductor and,therefore, large quantities of the melt material tend to have consider?able local temperature variations. Such temperature variations alsoproduce great variations in viscosity. For this reason it is verydifficult, it not impossible, to provide a coating of a relatively lowweight at high velocity operation.

In accordance with the present invention, the disadvantages of the priorart are avoided and an effective apparatus for coating with highlyviscous substances is provided. The invention includes a rotatableraster roll which extends into a reservoir containing the melt materialto be coated through an opening formed in the walls of the reservoir. Asthe surface of the roll emerges from the reservoir with the meltmaterialit is engaged by a wiper blade which is arranged substantiallycontacting the surface of the roller and the edge of the wiper bladecontacting the roller is directed opposite to the direction of rotation.The melt material is'supplied into the tank from the top thereof and itis maintained in the melted condition by heaters carried by the tank.The tank is advantageously supported on guides for horizontaloscillating movement along an axis in parallel with the axis of rotationof the raster roll.

Accordingly, it is an object of the invention to provide an improvedmeans for applying a coating to a web which includes a rotatable rasterroll over'which the web travels and with a portion of the rollscircumferential periphery extending through an opening in a reservoircontaining the coating material. The coating material is maintained in aproper melted condition and is wiped from the surface of the raster rollby a wiper blade positioned extending toward the surface of the roll.The wiper blades contact the surfaceof the raster roll at its point ofexit from the reservoir as it rotates.

A further object of the invention is to provide a' coating device which.is simple in design, rugged in construction and economical tomanufacture.

v The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating-advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which there is illustrated and described a preferredembodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS GENERAL DESCRIPTION OF THE PREFERREDEMBODIMENT In the drawings the apparatus illustrated includes arotatable raster roll 1 which is mounted for rotation in the directionof the arrow 13 about a horizontal axis. The raster roll is a steel rollwith a thin layer of chromium, for example, about 80 microns thick,plated on its circumferential periphery for protection against corrosionand rapid wear. Except for the opposite end portions, the entirecircumferential peripheral surface of the raster roll is worked toprovide a uniform arrangement of depressions or cells la, note FIG. 3.The depressions or cells can have a variety of shapes, such as invertedpyramids with quadrangular bases, inverted truncated pyramids withquadrangular bases and diagonal V-shaped grooves. The depressions orcells are formed in a raster roll by a molette, that is a working orengraving roll. Extending horizontally along one side of the raster rollis a tank 2 containing a quantity of a substance 6, such as wax or a hotmelt substance, for coating paper, tissue, cardboard, thermoplasticfilm, metal foil such as aluminum, and similar materials. An opening 2ais formed in the side and bottom of the tank adjacent the raster rolland the roll is positioned relative to the tank so that it extendslaterally through the opening into the body of the coating substance 6.As the raster roll 1 rotates, its circumferential peripheral surfacepicks up the coating substance from within the tank 2 in the depressionsor cells la.

As illustrated in FIG. 4, horizontally arranged guide members 4 and 5are secured to the ends of the tank 2 and extend into bushings 4a and50, respectively, mounted on a stationary frame 20. In addition, a motor22 with an eccentric cam, not shown, is mounted on the tank and a rodextends from the cam and is fixed to the frame 20. As the motor 22drives the cam, the rod which is fixed to the frame imparts areciprocating action to the tank so that is oscillates or reciprocatesin the horizontal direction supported and guided by the slidingengagement of the guide members 4 and 5 within the bushings 4a and 50.Accordingly, the tank moves in the horizontal direction with areciprocating or oscillatory motion relative to the raster roll 1.

As can be seen in FIG. 3, the horizontal dimension of the raster roll 1is greater than that of the tank 2 so that the ends 1b and 1c of theroll extend laterally beyond the upwardly extending ends 2b, 2c of thetank. The amount of reciprocating or oscillating movement of the tank issuch that its ends 2b, 2c do not extend beyond the corresponding endslb, 1c of the roll and, accordingly, there is no leakage from the tank.

Previously it was mentioned that the opposite ends of the raster roll 1,that is the ends lb and 1c, do not contain the depressions or cells In,and this is evident from FIG. 3. Further, the portions of thecorresponding ends 2b, 2c of the tank 2 which define the opening 2a,each have a Teflon coating 30 for facilitating the relative slidingaction between the tank and the raster roll and for preventing leakagefrom the tank.

On the opposite side of the tank 2 from its opening 2a, a side wall 14has upper and lower heating elements 11 and 12 for maintaining thetemperature of the coating substance 6 at a level sufficient to affordthe desired coating action. The coating substance 6 is supplied into thetank 2 in a liquid or melted condition through an inlet, not shown. Acover I0 closes the tank 2 at its top and can be removed for inspection,maintenance and operational purposes.

As the raster roll 1 rotates through the opening 2a in the tank 2, itsdepressions or cells la pick up the coating substance 6 and a doctor orwiper blade 3 is positioned at the exit side of the opening relative tothe direction of movement of the roll for removing any excess of thecoating substance from the surface of the roll and for retaining theexcess within the tank. The wiper blade 3 is formed of steel sheet. Thewiper blade is secured to and oscillates with the tank 2 by means of atongue or plate 8 which is held in position on the tank by screws 9.Further, one or more adjustment screws 7 are mounted in the lower end ofthe tank for providing fine adjustment of the wiper blade in respect tothe circumferential peripheral surface of the raster roll 1. As can benoted in FIGS. 1 and 2, the edge of the wiper blade which removes theexcess is directed against the raster roll so that it faces in thedirection opposite to the direction of rotation of the roll.

To assure a uniform temperature level throughout the body of the coatingsubstance 6 in the tank 2, one or more immersion heaters, not shown, arepositioned within the body of the coating substance.

In FIGS. 1 and 2 the operation of the apparatus is indicated with a webW of the material to be coated passing through the nip between theraster roll 1 and another roll 40 the direction of feed of the web andof rotation of the rolls is shown by arrows. As the raster roll rotatesthrough the opening 2a in the tank 2, it picks up the coating substance6 in its cells la and any excess on its surface is removed by the wiperblade as the roll exits from the opening at the lower end of the tank.As the roll rotates, the tank 2 and the wiper blade 3 oscillate orreciprocate in the horizontal direction relative to the roll ineffecting the filling of the cells In and the wiping of excess coatingsubstance from the surface of the roll.

As the raster roll rotates, its surface containing the cells in whichthe coating substance is located, comes into contact with the surface ofthe web \V at the nip between the rolls and the coating substance istransferred to the web as required. As an example of a typical coatingoperation, a cellulose paper of 58 g/m, travelling at a speed of 300m/minute is coated with 7 g/m, of Lunamelt HS 400 by the raster roll.Further, with this apparatus wax coatings of g/m, can be applied to thematerial to be coated. The temperature of the coating substance in themelted condition depends on the type of substance being used andgenerally ranges between 60 and C. As indicated above, the tank 2 isheated so that a uniform temperature is maintained throughout the bodyof the coating substance.

By the combination of the wiping action provided by the wiper blade,which retains any excess of the coating substance from the surface ofthe raster roll within the tank, and the oscillating movement of thetank and the blade, the problem experienced in the prior art, where airbubbles included in the coating interfered with the proper coatingaction, is overcome.

The sealing action afforded between the edges of the tank and thecorresponding ends of the raster roll against which the edges bear asthey oscillate back and forth, assures that the operation can proceedwithout any problem of leakage of the coating substance from the tank.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the inventiveprinciples, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. Web coating apparatus comprising a horizontally elongated tankcontaining a pool of fluid coating substance and said tank including apair of laterally spaced tank ends with a bottom member, and a backmember extending between said tank ends and defining an opening formedin said tank extending in the horizontal direction thereof and formed inthe lower portion of said tank ends and in an adjacent part of thebottom member and the opening arranged in communication with the pool ofcoating substance in the tank, a raster roll of a length longer thansaid tank having depressions formed in at least a portion of its centralcircumferential periphery and mounted for rotation about a horizontalaxis positioned adjacent said opening of said tank, said raster rollextending along said tank with a portion of its circumferentialperiphery projecting through the opening in said tank into the pool offluid coating substance therein, said tank ends disposed transversely ofthe axis of said roll and the lower portions of said tank ends beingcurved to complement and in sealing engagement with the curved surfaceof said roll means for oscillating said tank in the horizontal directionrelative to said roll, and an elongated wiper blade mounted on saidadjacent part of the bottom member of said tank and extending obliquelyof the bottom of said tank, the wiping edge of said blade locatedclosely adjacent to and extending along the circumferential periphery ofsaid roll at the point of emergence of the surface of said roll fromcontact with the pool of fluid coating substance for providing a wipingaction on the circumferential periphery of said roll, said blade ispositioned so that its wiping edge in contact with said roll facestoward said roll in the direction opposite to the rotation of said rollwhen the roll surface is moved downwardly past said bottom member, andmeans arranged for adjustably mountingsaid wiper blade on the bottomsurface of said tank and for providing a fine adjustment of its wipingedge relative to the circumferential periphery of said roll.

2. Web coating apparatus, as set forth in claim 1, wherein thecircumferential periphery of said raster roll having opposite endportions and a center portion extending between said end portions, thedepressions formed in the circumferential periphery of said raster rollarranged in a uniformly spaced manner over the center portion of thecircumferential periphery of said raster roll 3. Web coating apparatus,as set forth in claim 1, wherein said means for oscillating said tankcomprises a stationary frame, horizontally extending bushings fixed tosaid frame, horizontally extending guide members attached to said tankand slidably supported within said bushings, and means secured to saidtank and fixed ment to said tank.

UNITED STATES PATENT OFFICE" I v CERTIFICATE OF CORRECTION Patent No. v762 r 365 D t d October "2 1973.

Inventor(s) v eter 'Herzog It is certified that ex ror appears in theabove-identified patent '31; i that said Letters Patent are herebycorrected as shown below:

In the heading of the patent, insert:

--[30] Foreign Application Pr'iority'Deta' I January lo, 1969 Sweden...1 Io. 314E69 signedqendsealed this 1st day drain-wry 197A.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. RENE D;- TEGTMEYER o I I Attesting Officer ActingCommissioner? of Patents I FoRM po-m so (10-69)

1. Web coating apparatus comprising a horizontally elongated tankcontaining a pool of fluid coating substance and said tank including apair of laterally spaced tank ends with a bottom member, and a backmember extending between said tank ends and defining an opening formedin said tank extending in the horizontal direction thereof and formed inthe lower portion of said tank ends and in an adjacent part of thebottom member and the opening arranged in communication with the pool ofcoating substance in the tank, a raster roll of a length longer thansaid tank having depressions formed in at least a portion of its centralcircumferential periphery and mounted for rotation about a horizontalaxis positioned adjacent said opening of said tank, said raster rollextending along said tank with a portion of its circumferentialperiphery projecting through the opening in said tank into the pool offluid coating substance therein, said tank ends disposed transversely ofthe axis of said roll and the lower portions of said tank ends beingcurved to complement and in sealing engagement with the curved surfaceof said roll means for oscillating said tank in the horizontal directionrelative to said roll, and an elongated wiper blade mounted on saidadjacent part of the bottom member of said tank and extending obliquelyof the bottom of said tank, the wiping edge of said blade locatedclosely adjacent to and extending along the circumferential periphery ofsaid roll at the point of emergence of the surface of said roll fromcontact with the pool of fluid coating substance for providing a wipingaction on the circumferential periphery of said roll, said blade ispositioned so that its wiping edge in contact with said roll facestoward said roll in the direction opposite to the rotation of said rollwhen the roll surface is moved downwardly past said bottom member, andmeans arranged for adjustably mounting said wiper blade on the bottomsurface of said tank and for providing a fine adjustment of its wipingedge relative to the circumferential periphery of said roll.
 2. Webcoating apparatus, as set forth in claim 1, wherein the circumferentialperiphery of said raster roll having opposite end portions and a centerportion extending between said end portions, the depressions formed inthe circumferential periphery of said raster roll arranged in auniformly spaced manner over the center portion of the circumferentialperiphery of said raster roll.
 3. Web coating apparatus, as set forth inclaim 1, wherein said means for oscillating said tank comprises astationary frame, horizontally extending bushings fixed to said frame,horizontally extending guide members attached to said tank and slidablysupported within said bushings, and means secured to said tank and fixedto said frame for oscillating said tank in the horizontal direction withsaid tank supported by said guide members sliding in said bushings. 4.Web coating apparatus, as set forth in claim 3, wherein said meanssecured to said tank and fixed to said frame includes a motor mounted onsaid tank, a rod sEcured to said motor and fixed to said stationaryframe for effecting an oscillating movement as said motor is operatedfor transmitting the oscillating movement to said tank.